1. Field of the Invention
The present invention relates to a compact zooming lens system and a digital still camera using the compact zooming lens system, and more particularly to a compact zooming lens system and a digital still camera using the compact zooming lens system having a wide half angle of view and a high resolution.
2. Description of the Related Art
In recent years, digital still cameras or electronic cameras have rapidly come into widespread use in place of conventional cameras using silver film. A typical digital still camera shoots a subject with a solid image pickup device such as an image pickup device including a CCD (charge-coupled device), for example, and obtains image data including a still image and/or a motion image. The obtained image data is recorded in a digital fashion in a non-volatile memory or the like (e.g., a flash memory) provided to the digital still camera.
The market of digital still cameras is huge and, accordingly, user needs for such digital still cameras continue to expand in various directions. In particular, high image quality and downsizing (i.e., reduction in camera size) are constantly required and share a relatively large part of the user needs. A zooming lens system used as an image pickup lens system is also needed to satisfy the needs for both performance enhancement and for downsizing.
Regarding downsizing, a total lens length, which is a distance from a plane of a lens closest to the subject to an image plane, needs to be reduced. Further, regarding performance enhancement, an ultra fine resolution is required through an entire zooming range to cover at least three- to six-million elements of the image pickup device.
In addition, many users demand wide-angle lenses having wider angles of view, and thus a half view angle at a short focal length limit in a zooming lens should preferably be greater than 38 degrees. A half view angle of 38 degrees corresponds to a focal length of 28 mm in a 35-mm silver-film camera. Further, higher scaling factor of a zooming lens is required. A zooming lens having a focal length from about 35-mm to 135-mm in a silver-film is enough for ordinary purposes. Such a zooming lens has a scaling factor of about 4.8. Therefore, a zooming lens in a digital still camera should have a scaling factor at least as high as 4.8.
There are many kinds of zooming lens systems available for digital still cameras. Among these is a zooming lens system which is suitable for a compact digital still camera system that includes, arranged sequentially from a subject side, a first optical lens group having a negative focal length, a second optical lens group having a positive focal length, and a third optical lens group having a positive focal length. This zooming lens system further includes an aperture diaphragm which is mounted to the subject side of the second optical lens group in a manner such that the aperture diaphragm and the second optical lens group are integrally movable. Further, when the scaling of the zooming lens system is changed, for example, from the short focal length limit to the long focal length limit, the second optical lens group moves away from the image side to the subject side and, at the same time, the first optical lens group moves in such a way that a displacement of the image plane caused by the scaling change is corrected. The above-described zooming lens system is described in Japanese Laid-Open Patent Application Publication Nos. 10-39214 and 10-104518, and in U.S. Pat. No. 6,498,687. However, such a zooming lens system is not suitable for a high scaling factor more than 4.0.